Bow building is so easy, even a caveman can do it. Cavemen didn't have scales, polyurethane or tillering trees. Those are just designed to make our work easier.
Checking poundage can be done with a bucket filled with water, a bathroom scale, or a scale bought online for as little as $10.
You need to see the bend in a bow as it is being bent. Floor tiller will get you a long way. The last bit of tillering can be done with a tillering stick, or with the use of the reflection from a mirror/big window.
Finishing the bow does not necessarily increase lifespan. It does help is keeping moisture and dirt out. Finish the bow with any type of oil, varnish or even grease.
Drawlength depends on the archer, not the bow. The bow determines the maximum drawlength you can safely get from a bow. You can design a bow so it is optimal for the archer's drawlength.